Referring to FIG. 1, there is illustrated a known antenna sharing frequency-division duplex (FDD) radio system. The FDD radio system 10 includes a shared antenna 12 with duplexer 14 having transmit and receive filters, 16 and 18, respectively. The transmit frequency and receiving frequency needs to be well separated so that the duplexer can have a good isolation between transmit and receive chains. The system also includes an intermediate frequency transceiver 20 having a transmit side 22, a receive side 24 and a master oscillator 26. The system also includes a base band component 30 with analog to digital converter 32 and digital down converter 34 on the receive path and digital up converter 36 and digital to analog converter 38 on the transmit path. The base band component 30 includes baseband processor 40. The FDD radio system 10 of FIG. 1 typically splits the available bandwidth between the transmit side and the receive side. For the example of FIG. 1 the transmit side uses 1930 to 1990 MHz, while the receive side uses 1850 to 1910 MHz.
As illustrated in FIG. 1, frequency-division duplex (FDD) radios can be co-located. Consequently, they have found it desirable to share an antenna.
Referring to FIG. 2, there is another known antenna sharing system for synchronous time-division-duplex (TDD) where transmit and receive use the same frequency but in different time intervals. All the radios are synchronized in transmit or in receive via a network or a global-positioning-system (GPS). As illustrated in FIG. 2, a 10 ms time frame is divided into 4 parts. The first part 60 is for all the base station radios to transmit and all the terminals to receive; the second part 80 is a transition gap to allow transceivers to switch from transmission mode to reception mode; the third part 10 is the time interval that all the terminals can transmit while all the base stations should be in receiving mode; the fourth part 120 is the receive to transmit transition gap. So all the radios are synchronized either in transmission mode or in receiving mode.
However, when co-located TDD radios are in asynchronous mode, one radio is in transmit mode with signal strength 23 dBm, while the other is in receiving mode with a desired weaker signal (˜−90 dBm), there requires roughly 110 dB of isolation in between transmitting radio and receiving radio so that the receiver can work properly.
Referring to FIG. 3, there is graphically illustrated USA TV channel allocation prior to conversion from analog to digital TV transmission. As can be seen Channels 2 to 69 were allocated between 54 MHZ and 806 MHz with gaps 200, 202, 204 and 206 between 72 MHZ and 76 MHz, 88 MHz and 174 MHz, 216 MHz and 470 MHz and 608 MHz and 614 MHz, respectively.
Referring to FIG. 4, there is graphically illustrated USA TV channel allocation after conversion from analog to digital TV transmission. As can be seen Channels 2 to 51 were allocated between 54 MHZ and 698 MHz with the same gaps 200, 202, 204 and 206 between 72 MHZ and 76 MHz, 88 MHz and 174 MHz, 216 MHz and 470 MHz and 608 MHz and 614 MHz, respectively.
Systems and methods disclosed herein provide a system for antenna sharing to obviate or mitigate at least some of the aforementioned disadvantages.